1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly to a voltage regulator circuit of a semiconductor memory device that operates at a low voltage.
2. Description of the Prior Art
The designed operating voltages of semiconductor memory devices are becoming lower, in order to increase integration and to decrease power consumption. Accordingly, increasingly lower external voltages are used to operate the devices, but that is not always enough. Thus voltage regulators are also used to convert the external voltage to the lower operating voltage of the device.
In the 1994 IEEE Symposium on the Low Electricity Electronical Engineering, a paper titled "Low-dropout On-chip Voltage Regulator for Low-Power Circuits" teaches to use a NMOS driver in the regulator of the semiconductor memory device. The paper teaches to use a boosting circuit to increase the voltage level of the control signal applied to the gate of the NMOS driver, as well as a clock signal generating circuit to operate the boosting circuit.
A problem is that, as operating voltages decrease further, a high external voltage is applied to the regulator can destroy the transistors of the boosting circuit and the clock signal generating circuit. The reason is that high voltage differences will be applied across the junctions of the transistors.